The present invention relates to a constant flow regulating device having an inlet chamber and an outlet chamber.
Many diseases may be diagnosed by studying the concentration of certain substances, for example nitric oxide, in the exhalation air of a person. However, since the pressure of the exhaled air varies from person to person, the volume of air passing through a test tube or the like per unit of time will vary considerably. There is therefore a need for a device that will create a constant flow of exhaled air to a test tube or the like independent of the pressure of the exhaled air. The object of the present invention is to provide such a device.
This object is obtained by a constant gas flow regulating device having an inlet chamber and an outlet chamber, a movable wall delimits the inlet and outlet chambers from each other, said wall comprising an opening permitting communication between said chambers, an elongate element extends centrally in the opening in the movable wall in the moving direction thereof, in a first position the opening in the movable wall is placed in the vicinity of a first end of the elongate element, said element having a sectional size that is gradually increasing from the first to a second end thereof, the size of the opening in the movable wall is larger than the sectional size of the elongate element, characterised in that a helical spring for biasing the movable wall towards a first position is provided and that a body attached to the movable wall and containing the opening surrounding a portion of the elongate element is slidably connected with an elongate guiding member defining the moving direction of the movable wall.
By such a device the space between the outer periphery of the elongate element and the inner periphery of the opening in the wall will decrease proportionally to the increase in pressure in the inlet chamber so that the pressure in the outlet chamber will be held constant independent of the pressure in the inlet chamber.
In the preferred embodiment the elongate element has a first end disposed in the inlet chamber and a second end disposed in the outlet chamber. The sectional shape of the elongate element corresponds to the sectional shape of said opening, the sectional shape of the opening in the movable wall and of the elongate element being circular and the elongate element having the shape of a truncated cone. The movable wall can be a diaphragm. Preferably the constant flow is in a range between 0.5 and 4.5 1/min and more preferably between 0.6 and 3 1/min.